This invention relates to an optical circuit and speaking more in detail, to a so-called photosensor including a light emitting element and a photosensitive element in order to detect an object in an optical manner.
Heretofore so-called photosensors are used for the purpose of detecting optically cards or sheets, or obtaining pulses by means of a disk having radial slits and secured to the rotating shaft of a motor.
A kind of photosensors hitherto widely utilized is described e.g. in Application Manual [Photointerrupter] SHARP (January, 1982) p. 26, FIG. 4-7(d). In this circuit a current is made flow through a light emitting diode from a power source +V.sub.cc through a resistor R and a voltage is applied to a phototransistor from the power source +V.sub.cc through another resistor. The light emitting diode emits light, when a current flows therethrough and the phototransistor is switched-on, when the light reaches it so that a current flows through this phototransistor from the power source +V.sub.cc. Since the current amplification factor of the phototransistor is small, its output is amplified by a transistor in the succeeding stage and a waveform having a large amplitude is taken out. However, since the waveform includes distortions, the amplified output is further shaped in waveform by means of a Schmitt trigger element.
In addition, in this circuit structure, since the circuit comprising the light emitting element and that comprising the photosensitive diode are separated from each other with respect to the power supply, the interface for taking out the output should consist of 3 lines; i.e. power source line, collector line and earth line for the phototransistor.
Recent electronic apparatuses have a tendency to become more and more highly functional and many photosensors are incorporated here and there in the apparatuses. Consequently, since the number of interface signal lines increases proportionally thereto, assembling work for the signal lines in the apparatuses becomes tremendous.